FILA: F INE - GRAINED I NDOOR L OCALIZATION Kaishun Wu, Jiang Xiao, Youwen Yi, Min Gao, and Lionel M. Ni INFOCOM Sowhat

O UTLINE Introduction System Design Evaluation Discussion Conclusion

O UTLINE Introduction System Design Evaluation Discussion Conclusion

M OTIVATION WiFi-based indoor localization RSSI range-based localization Multipath Variance of RSSIs – 5dB in 1 min at immobile receiver

Capable to eliminate multipath effect O BJECTIVE An alternative metric to RSSI Stabl e

O UTLINE Introduction System Design Evaluation Discussion Conclusion

F OUNDATION OF FILA OFDM CSI Orthogonal Frequency Division Multiplexing Channel State Information

OFDM Multicarrier modulation scheme for wideband wireless communication Modulate data on multiple subcarriers in different frequencies Transmit simultaneously

CSI Channel state/status information Fine-grained value from the PHY layer 1. Describe how a signal propagate from TX to RX 2. Represent combined effect of scattering, fading and power decay with distance Channel properties of each subcarrier Amplitude Phase

S YSTEM A RCHITECTURE CSI Processing Calibration Location Determinatio n

CSI P ROCESSING CSI P ROCESSING T IME - DOMAIN M ULTIPATH M ITIGATION n bandwidth ~40MHz > coherence bandwidth  resolvable reflections 1. IFFT – channel response in frequency  time domain 2. Filter – keep 1 st cluster truncation threshold = 50% of 1 st peak value 3. FFT – channel response in time  frequency domain CSI Processing Calibration Location Determinatio n

CSI P ROCESSING CSI P ROCESSING F REQUENCY - DOMAIN F ADING C OMPENSATION Prob. of simultaneous deep fading occurring on multiple uncorrelated fading envelopes > deep fading occurring on a single freq. system ∵ channel bandwidth of n > coherence bandwidth ∴ freq.-selective fading across all subcarriers  uncorrelated Reduce the variance in CSIs owing to small scale factors Weighted average CSI Processing Calibration Location Determinatio n

C ALIBRATION Relationship between CSI eff and distance σ : environment gain of baseband to RF gain of RF band to baseband antenna gain n : path loss fading exponent Fast training algorithm 1. 2 anchors for training 2. Another anchor for testing CSI Processing Calibration Location Determinatio n

L OCATION D ETERMINATION 1. APs’ coordinate info. from network layer 2. Distance between AP/object Effective CSI Refined radio propagation model Trilateration! CSI Processing Calibration Location Determinatio n

O UTLINE Introduction System DesignEvaluation Discussion Conclusion

H ARDWARE CONFIGURATION AP : TP-LINK TL-WR941ND 2.4~2.4835GHz Receiver: HP laptop with 2.4GHz dual-core CPU Intel WiFi Link n NICs Modified driver to collecting CSI values from NICs Placed on a plastic cart

E XPERIMENTAL S CENARIOS 1. Chamber 3m x 4m Ideal free space indoor environment (only LOS signal exist without multipath reflections) 2. Research laboratory 5m x 8m 3 APs Weekday afternoon (students seating or walking around)

E XPERIMENTAL S CENARIOS 3. Lecture theatre 20m x 20m 4. Corridor 32.5m x 10m Cover corridors, rooms and cubicles Impact of the absence of LOS APs

R OBUSTNESS OF T HE R EFINED M ODAL

T EMPORAL S TABILITY OF CSI

D ISTANCE D ETERMINATION A CCURACY Chamber Research laboratory Lecture theatre 10 different locations Positions with serious multipath effect – Accuracy: FILA > RSSI-based by 10 times Mean distance error

L OCALIZATION A CCURACY IN S INGLE R OOM Research laboratory Lecture theatre 90% - 1m/1.8m ; median m/1.2m

L OCALIZATION A CCURACY IN M ULTIPLE R OOMS Corridor 6 APs in multiple rooms Experiment procedure Offline training Fix the position of the object at reference nodes  collect APs’coordinates and CSI 1m/s Collect 20 CSIs and RSSIs at each position Robust, median = 1.2m

L ATENCY Latency = calibration + determination phase Calibration Data collection AP transmit message every 0.8ms Collect 20 CSIs 20 * 0.8 = 16ms Calibration processing = 2ms Determination IFFT, FFT with wireless NICs= ignorable Signal processing + trilateration = 2ms Total: 16ms + 2ms + 2ms = 20ms

O UTLINE Introduction System Design EvaluationDiscussion Conclusion

D ISCUSSION CSI + fingerprint-based method  more accurate localization Leverage available multiple APs to improve accuracy Implement FILA on smart phone

O UTLINE Introduction System Design Evaluation DiscussionConclusion

C ONCLUSION Design and implement FILA CSI with OFDM system Compared to RSSI-Based in different scenarios Capable to deal with multipath effect (time domain processing) Stable (freq. domain processing) Disadvantage Unclear descriptions Comparison of single room/multiple room

T HANKS FOR L ISTENING ~